As a bending machine for bending a pipe (pipe material) to a predetermined curvature, for example, a bending machine is known which includes a first supporting portion configured to support a part of a pipe on one end side thereof and a second supporting portion configured to support a part of the pipe on the other end side thereof, and which is configured to bend the pipe along an arc-shaped guide face provided on the first supporting portion by rotating the first supporting portion about a predetermined rotation axis and also causing the second supporting portion to linearly move.
Such a bending machine is equipped with a mandrel for preventing the deformation (flattening) of a pipe at bending, and a pipe is bent with the mandrel inserted in the pipe.
In the bending of a pipe using a mandrel, lubricant oil is used in some cases to reduce the sliding friction between the inner surface of the pipe and the mandrel and to prevent the formation of scratches on the inner surface of the pipe. However, since the lubricant oil is attached to the inner surface of the pipe, the bending using lubricant oil requires a washing operation for removing the lubricant oil by washing the inside of the pipe after the bending.
Here, to avoid the use of lubricant oil at the bending of a pipe and to eliminate the need for the washing operation for removing the lubricant oil, a technique has been developed in which a synthetic resin such as MC nylon is provided to a front end portion of a mandrel. The technique in which a synthetic resin such as MC nylon is provided is described in, for example, Patent Literature 1.